It is standard practice, as for example described in U.S. Pat. 4,266,719 and the references cited thereagainst, to mount a railway rail on at least one insert which is received in a recess formed in a normally concrete rigid base that is fixed on the ground. A layer of an elastomer is provided between the insert and the side and end flanks of the recess to suspend the insert in the recess. The elastomer damps sound transmission between the rail and the base, allowing a train to run along the rail substantially more silently than would otherwise be possible.
The recess and insert are normally complementarily shaped, and are both normally also symmetrical about a pair of mutually perpendicular vertical symmetry planes, one extending parallel to and through the center of the rail they support and the other extending perpendicular through the rail they support. The angle these flanks form with the vertical is the same. The stress they are subject to is, however, not the same. Nonetheless when such inserts and bases that are symmetrical as described above are employed a flank angle is chosen which is a compromise that more or less is satisfactory for each flank of the insert.
The problem with such arrangements is that they occasionally fail, with the elastomeric bodies shearing on one flank or the other. Attempts to refigure the flank angle to eliminate such failure at one flank normally simply lead to failure at another flank.